Re: [PATCH 09/15] swiotlb: make the swiotlb_init interface more useful

[Christoph Hellwig <hch@xxxxxx>]

On Wed, Jun 01, 2022 at 11:11:57AM -0700, Nathan Chancellor wrote:
> On Wed, Jun 01, 2022 at 07:57:43PM +0200, Christoph Hellwig wrote:
> > On Wed, Jun 01, 2022 at 10:46:54AM -0700, Nathan Chancellor wrote:
> > > On Wed, Jun 01, 2022 at 07:34:41PM +0200, Christoph Hellwig wrote:
> > > > Can you send me the full dmesg and the content of
> > > > /sys/kernel/debug/swiotlb/io_tlb_nslabs for a good and a bad boot?
> > > 
> > > Sure thing, they are attached! If there is anything else I can provide
> > > or test, I am more than happy to do so.
> > 
> > Nothing interesting.  But the performance numbers almost look like
> > swiotlb=force got ignored before (even if I can't explain why).
> 
> I was able to get my performance back with this diff but I don't know if
> this is a hack or a proper fix in the context of the series.

This looks good, but needs a little tweak.  I'd go for this variant of
it:


diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index dfa1de89dc944..cb50f8d383606 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -192,7 +192,7 @@ void __init swiotlb_update_mem_attributes(void)
 }
 
 static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
-                                   unsigned long nslabs, bool late_alloc)
+               unsigned long nslabs, unsigned int flags, bool late_alloc)
 {
        void *vaddr = phys_to_virt(start);
        unsigned long bytes = nslabs << IO_TLB_SHIFT, i;
@@ -203,8 +203,7 @@ static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, 
phys_addr_t start,
        mem->index = 0;
        mem->late_alloc = late_alloc;
 
-       if (swiotlb_force_bounce)
-               mem->force_bounce = true;
+       mem->force_bounce = swiotlb_force_bounce || (flags & SWIOTLB_FORCE);
 
        spin_lock_init(&mem->lock);
        for (i = 0; i < mem->nslabs; i++) {
@@ -275,8 +274,7 @@ void __init swiotlb_init_remap(bool addressing_limit, 
unsigned int flags,
                panic("%s: Failed to allocate %zu bytes align=0x%lx\n",
                      __func__, alloc_size, PAGE_SIZE);
 
-       swiotlb_init_io_tlb_mem(mem, __pa(tlb), nslabs, false);
-       mem->force_bounce = flags & SWIOTLB_FORCE;
+       swiotlb_init_io_tlb_mem(mem, __pa(tlb), nslabs, flags, false);
 
        if (flags & SWIOTLB_VERBOSE)
                swiotlb_print_info();
@@ -348,7 +346,7 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
 
        set_memory_decrypted((unsigned long)vstart,
                             (nslabs << IO_TLB_SHIFT) >> PAGE_SHIFT);
-       swiotlb_init_io_tlb_mem(mem, virt_to_phys(vstart), nslabs, true);
+       swiotlb_init_io_tlb_mem(mem, virt_to_phys(vstart), nslabs, 0, true);
 
        swiotlb_print_info();
        return 0;
@@ -835,8 +833,8 @@ static int rmem_swiotlb_device_init(struct reserved_mem 
*rmem,
 
                set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
                                     rmem->size >> PAGE_SHIFT);
-               swiotlb_init_io_tlb_mem(mem, rmem->base, nslabs, false);
-               mem->force_bounce = true;
+               swiotlb_init_io_tlb_mem(mem, rmem->base, nslabs, SWIOTLB_FORCE,
+                               false);
                mem->for_alloc = true;
 
                rmem->priv = mem;